1. Field of the Invention
The present invention relates to culturing marine species, and more particularly, to culturing crabs in a recirculating marine aquaculture process.
2. Description of Related Art
In recent years the world has witnessed an alarming decline in commercial fisheries, the result of over fishing and environmental degradation. According to the Food and Agriculture Organization (FAO) of the United Nations, nearly 70% of the world""s commercial marine fisheries species are now fully exploited, overexploited or depleted.
Based on anticipated population growth, it is estimated that the world""s demand for seafood will double by the year 2025. Therefore, a growing gap is developing between demand and supply of fisheries products, which results in a growing seafood deficit. Even the most favorable estimates project that in the year 2025 the global demand for seafood will be twice as much as the commercial fisheries harvest.
The same trend is present in the U.S. per capita consumption of seafood by Americans that increased 25% from 1984 to 1994, and continues to increase. As a result, the United States has become highly dependent on imported seafood. The U.S. is, after Japan, the world""s largest importer of seafood. The value of fish imports increased by nearly 80% between 1985 and 1994 to a record level of nearly $12 billion U.S. This has resulted in a trade deficit of $7 billion U.S. for edible seafood, which is, after petroleum, the largest contributor to the U.S. trade deficit among natural products and the largest deficit among all agricultural products.
It is very clear that the only way to meet the world""s growing needs in fisheries products, and to reverse the U.S. fisheries trade deficit, is through marine aquaculture systemsxe2x80x94the farming of aquatic organisms in controlled environments. In response to the situation, global aquaculture production is expanding quickly. Aquaculture""s contribution to the world""s seafood supplies increased from 12 to 19% between 1984 and 1994. U.S. aquaculture production has also grown steadily in the 1980""s and 1990""s and it is the fastest growing agricultural industry. However, despite the recent growth of the U.S. industry, only 10% of the seafood consumed in the U.S. comes from domestic aquaculture, and the U.S. ranks only tenth in the world in the value of its aquaculture production.
Worldwide, it is estimated that in order to close the increasing gap between demand and supply of aquatic products, aquaculture will need to increase production three-to-four-fold during the next two and a half decades. In this context, there is a compelling motivation to develop aquaculture systems of improved and commercially viable character for high volume production of aquatic species and environmental sustainability.
Crab fisheries have been an important part of local and regional economies for generations. Notable examples are the blue crab (Callinectes sapidus) in the Chesapeake Bay region, the Alaskan (red) King crab (Paralithodes camtschatica) in the Bristol Bay region of the Bering Sea, and the various Cancer crab species (i.e., the Dungeness crab, Cancer magister, the Jonah crab, C. boresalis and the Rock crab, (C. irraoratus) along the Pacific coast of the United States. As with many marine species, most of these crab fisheries exhibit severe fluctuations in stock abundance and, correspondingly, their respective harvest.
The culture of some of the above species, such as Callinectes and Cancer species, has been previously investigated, but not actively undertaken. For the most part, culture of these crabs species has been discounted because of a variety or reasons including complex and multiple larvae stages, cannibalism during juvenile stages, slow growth rate to market size and the impracticality of relying on wild-caught broodstock. In addition, environmental considerations e.g., discharge of environmentally-disruptive effluents, or limitations on culture because of environmental regulations, have probably discouraged development of commercial facilities.
With depleted crab resources worldwide, most notably the recent decline of the Chesapeake bay blue crab stock and harvests, and increased fishing efforts on the dwindling crab fisheries, it is critical to ensure the long-term sustainability of the various crab species and the local crab industries they support.
With the many challenges to blue crab reproduction and larval growth in the wild, it is clear that new approaches must be explored to ensure the viability of the blue crab resource. Given the difficulty-and often impossibility-of controlling environmental factors, it is necessary to research and develop ways to spawn and nurture blue crabs in captivity that can be released into the Chesapeake Bay when they are capable of surviving on their own. Additionally the captive culture of blue crab for commercial consumption should be reinvestigated. Especially, in order to meet current market demand, and hopefully, decrease current fishing pressure on this species. It should be noted that other research institutes (e.g., Australia""s Bribie Island Aquaculture Research Center) are exploring hatcheries for different crab species such as the mud crab (Scylla serrata), but these studies are focused in open pond environments as opposed to inside a highly controllable, predictable, and reliable closed-loop environment.
Given the increasing state and federal regulation of natural fisheries and the aquaculture industry, and the increasing demand for crabmeat, it is important for crab-producing states to develop competitive and sustainable crab aquaculture capabilities. Although aquaculture is still a relatively new industry in this country, it is increasing in importance and has the potential for major growth in the 21st century.
In an effort to eliminate the effects of marine aquaculture on the environment and to optimize aquaculture production, a new environmentally acceptable aquatic farming technology has recently emerged: the use of recirculated marine aquaculture systems (RMAS), in which the same water is continuously reused in operation of the system. These systems have many advantages over non-recirculating systems.
Water re-use in the RMAS minimizes any adverse environmental burden created by the aquaculture system since there is minimal net waste material generation, and what waste is generated is easily handled by local sewer systems. RMAS offer flexibility in location options (urban, rural, inland) since they are not confined to coastal areas or open oceans. Unlike free-floating pens, process conditions can be better controlled within a RMAS.
In general, aquaculture systems of the prior art are poorly integrated in respect of the life stages of the aquatic species of interest and the process conditions associated therewith. As a result, the commercial aquaculture systems developed to date are highly variable in efficiency and output of product. Such systems are subject to numerous processing and operational deficiencies, including: sub-optimal production of fish; absence of control of process conditions; process instability; susceptibility to environmental pathogens; susceptibility to pollution; loss of stock; and the lack of well-defined optimal conditions for achieving maximal growth and production of the aquatic species being raised in the aquaculture system.
There is therefore a basic need in the art of aquatic farming, especially for culturing crabs for aquaculture systems of improved character, for high performance production of crabs.
In respect of the present invention, as hereinafter more fully described, the following references are noted, and their disclosures hereby incorporated herein by reference:
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The present invention relates to aquaculture production of a marine species in a recirculating marine aquaculture process system for achieving optimal yield of the marine species at variable density grow-out conditions. Preferably, the marine species is a crustacean including, but not limited to, crayfish, crabs, lobster and shrimp.
As used herein, the term xe2x80x9cregimexe2x80x9d refers to concurrent changes of parameters of the process (e.g., photoperiod, temperature, salinity, dissolved oxygen, population density). Such concurrent changes of process parameters are employed to achieve a regulated process in specific stages or steps of the aquaculture process.
The closed, recirculating marine aquaculture process of the invention involves simultaneous manipulation and then continuous monitoring and control of three key process factors: (1) photoperiod, (2) water temperature, and (3) water chemistry (salinity, dissolved oxygen (DO), ozone level, pH, etc.). For each species of crab, these process conditions are manipulated/tailored to achieve optimal performance.
In accordance with one aspect of the invention, distinct process conditions are applicable to a specific crab species including changing photoperiod (light exposure) conditions according to the spawning and lifecycle of the crab.
In another aspect, the invention relates to a recirculating marine aquaculture process for production of a crab species, including (i) crab broodstock conditioning, (ii) spawning, (iii) egg incubation, (iv) larval growth, (v) nursery post-larval growth, and (vi) grow-out of crab to a final product weight, in which each stage (i)-(vi) of the process involves operation in an aqueous medium that is coupled in liquid recirculation relationship with means for removing waste components from the aqueous medium and returning purified aqueous medium to the external environment. The process involves operation in a closed, recirculating aquaculture system in which photoperiod, water temperature, water chemistry, and diet are optimized and then continuously monitored and controlled to obtain optimal production at each of the six phases (i)-(vi) of the life cycle.
The process includes the steps of:
providing recirculated aqueous media tanks for populations in the life-cycle stages for crab production;
optionally administering, as needed, gonadotropin-releasing hormone or GNRH agonist to a broodstock population of the crabs prior to spawning;
continuously recirculating aqueous medium and treating the aqueous medium for removal of waste therefrom;
maintaining process conditions in said aqueous media for the life-cycle stages in accordance with PROCESS CONDITIONS correlative to LIFE-CYCLE STAGE in Table A below:
In another aspect, the invention relates to a process for producing a crab species, by cultivation in life-cycle stages including broodstock conditioning, spawning, egg incubation, larval rearing, nursery processing, and grow-out, in a continuous recirculation aquaculture system adapted to culture corresponding populations of broodstock, eggs, larvae, and crabs in aqueous media, wherein photoperiod, water temperature, water chemistry, and diet are optimally maintained in the life-cycle stages to achieve optimal production in such life-cycle stages.
Water may be supplied for the process from a municipal water supply following de-chlorination treatment, e.g., by contacting the municipal water with activated carbon sorbent, to constitute the aqueous medium for the broodstock conditioning, spawning, egg incubation, larval rearing, nursery processing, and grow-out life-cycle stages.
Another aspect of the invention relates to a process of grow-out of a crab species in an aqueous medium, including the steps of:
(a) culturing the crab species in a culture tank coupled in liquid recirculation flow relationship with a biofilter and mechanical filter maintained under aerobic microbial conditions;
(b) continuously circulating aqueous medium through the culture tank and the biofilter and mechanical filter coupled therewith, to remove nitrogenous wastes and solids from the aqueous medium and produce a filtered aqueous medium for recirculation to the culture tank;
(c) maintaining a circulation rate of the continuously circulating aqueous medium producing from about 0.5 to about 5 volumetric changes of the culture tank per day;
(d) maintaining dissolved oxygen at about 80% to about 100% saturation in the aqueous medium in the culture tank;
(e) exposing grown out crabs in the culture tank aqueous medium to a photoregime whose light period substantially exceeds duration of light exposure in a wild marine environment; and
(f) utilizing a hyposaline aqueous medium as the aqueous medium.
Yet another aspect of the invention relates to a method of producing a crab species in a recirculating aquaculture system comprising:
(i) respective aqueous medium-containing tanks for successive life-cycle stages of the crab species including broodstock conditioning, spawning, egg incubation, larval rearing, nursery processing, and crab grow-out, and
(ii) filtration means coupled in closed loop aqueous medium recirculation relationship with the respective tanks, so that aqueous medium from a tank is filtered for purification thereof and returned to the tank.
In such process, growth conditions are maintained in each of the respective tanks by the steps of:
(a) administering nutritive material to each of the respective tanks containing the crab or crab precursor feeding species;
(b) maintaining salinity, dissolved oxygen, pH, temperature and photoexposure within predetermined ranges in each of the respective tanks;
(c) utilizing a hyposaline aqueous medium as the aqueous medium in the grow-out tank; and
(d) optionally administering, as needed, gonadotropin-releasing hormone (GnRH) or GnRH agonist (GnRHa) to the crab species in a sustained release form prior to spawning of the crab species in the spawning tank.
With respect to the optional administration of GnRH or GnRHa for enhancement of spawning capabilities, it will be appreciated that aquatic species will vary substantially in their need for, and response to, such hormonal treatment, and that some marine species may not require any such augmentive treatment for carrying out spawning in an optimal manner. The dose, dose schedule, and manner and form of administration may all be varied selectively in achieving optimal spawning behavior, with optimal hormonal treatment being readily empirically determined within the skill of the art. Preferably, GnRHa is administered in a sustained release form at a dose in a range of from about 25 to about 100 micrograms per kg body weight of females, and at a dose in a range of from about 15 to about 30 micrograms per kg of body weight of males.
Yet another aspect of the present invention relates to producing and harvesting soft shell crabs. Molting of crabs occurs many times through the life of the crab. Marine data suggests that there may be one or two peak molting periods during the years but not all individual crabs adhere to this schedule. At the time of molting, the crab backs out of the old shell and remains hidden for the next few days until the new shell hardens. It is known that capturing the early stage soft-shell crabs in baited traps is very difficult because of the natural instinct of the crabs to remain buried in sediment. More important, in many states there is requirement to release soft shell crabs that are trapped in the wild. Thus, the present invention provides for a system that includes harvesting of soft-shell crabs by monitoring of pre-molting crabs and segregation of them until shedding, at which time they can be removed from the tanks for marketing.
The same conditions noted above are applied for the production of soft shell crabs. Pre-molt crabs can be segregated and held in the cyclical cage system referenced above. Pre-molt crabs can be identified by a thin white, pink or red line on the inside edge of the swimming paddles. Water quality condition must be optimally maintained as discussed in Stickney (2000), the content of which is hereby incorporated herein by reference for all purposes.